The replacement of synthetic polymeric materials with naturally derived and biodegradable polymers is an important goal in achieving sustainable products and material processes. Among all potential natural starting materials, those that are most prevalent in nature and easily captured, separated, and purified are also the most cost-effective replacement options. Materials such as wood, natural fibers, natural oils, and other natural chemicals are all readily available in bountiful amounts. Heretofore, the limitations in using natural materials more broadly are due primarily to limitations in processing flexibility (e.g. moldability) and/or ultimate properties (e.g. strength, elongation, modulus).
Natural animal-hide leather is a versatile material for which there are few synthetic alternatives that meet the same performance attributes. Natural animal-hide leather in particular has a unique blend of flexibility, puncture resistance, abrasion resistance, formability, breathability, and imprintability. Synthetic leather substitute materials are known in the art. Many utilize a fabric backing and a polyurethane or plasticized polyvinyl chloride elastomeric surface—such material constructions may achieve certain performance attributes of natural animal-hide leather but are not all-natural and are not biodegradable. It is desirable to have a different material that comprises all-natural materials or at least contains a substantial portion of all-natural content. Furthermore, it is desirable that any leather substitute be biodegradable to avoid disposal concerns.
Memory foam materials are entirely made of synthetic polymers today. For example, most commercial memory foam comprises polyurethane elastomer that utilizes foam structure. Memory foam materials are characterized by lossy behavior, i.e. the polymer has a high loss modulus (tan δ). Memory foam materials are generally very stiff at temperatures substantially below room temperature (e.g. below 10° C.), rubbery at temperatures substantially above room temperature (e.g. above 50° C.), and leather/lossy at or near room temperature (e.g. 15° C.-30° C.).
Liu (U.S. Pat. No. 9,765,182) discloses an elastomeric product comprising epoxidized vegetable oil and a polyfunctional carboxylic acid. Because such ingredients are not miscible in each other, Liu discloses the use of an alcohol solvent that is capable of solubilizing the polyfunctional carboxylic acid and that is miscible with the epoxidized vegetable oil. An exemplary epoxidized vegetable oil disclosed by Liu is epoxidized soybean oil. An exemplary polyfunctional carboxylic acid disclosed by Liu is citric acid. Exemplary alcohols used as a solubilizing agent include ethanol, butanol, and isopropyl alcohol. Liu discloses the creation of an elastomer by dissolving citric acid in ethanol and then adding the entire amount of epoxidized soybean oil to the solution. The solution is then heated to 50° C.-80° C. for 24 hrs to remove the ethanol (assisted by vacuum). Liu discloses that the optimal temperature range for polymerization occurred at 70° C. (without any catalysts). The Liu disclosure is clear that the evaporation temperature range for the alcohol solvent and polymerization temperature are overlapping and thus there exhibits a high risk of prematurely curing the polymer, i.e. forming a gel, before the entirety of the solvent is removed. We have found that elastomers prepared by the method disclosed by Liu contain substantial porosity due to the evaporation of residual alcohol solvent after the onset of polymerization.